The invention relates to a control arrangement for a gear shift transmission of a motor vehicle wherein a shift piece is longitudinally slidable on a shifting shaft by a selector lever fastened to a preselector shaft and is non-rotatably connected with the shifting shaft. The shift piece controls shifting forks assigned to individual transmission gears and engages synchronizing clutches through a shift finger interacting with several shift rails disposed next to one another. A locking system is provided so that when one shift rail is moved, the remaining shift rails are locked.
A similar type control arrangement for a gear shift transmission is described in the journal Sport Auto, 4/1988, Page 127. There a first Bowden cable is controlled by the gear shift lever to preselect the transmission gears and a second Bowden cable shifts the individual transmission gears through shift forks and synchronizing clutches. A control arrangement known from DE-PS 31 25 632, is used as the connection from the shift forks to the preselector shaft and the shifting shaft is controlled by the Bowden cables. The shifting shaft is equipped with a radially projecting shift finger which engages in recesses of shift rails forming shifting lanes. The shift rails affecting the shift forks can be moved transversely with respect to the shifting shaft. A sliding of the shift finger in the direction of the axis of the shifting shaft preselects the transmission gears. A swivelling of the shift finger shifts the transmission gears. The shift rails disposed next to the selected shifting lane are each blocked by cams which are constructed in one piece with the shift finger and rest against circular-arc-shaped wall parts of the shift rails on the inside.
In order to achieve a compact construction of the shifting arrangement, the shift finger must be constructed to be as short as possible. The swivelling angle of the shift finger (required for the shifting) therefore becomes relatively large so that during swivelling, the effective lever arm is considerably shortened in an undesirable manner.
It is an object of the invention to provide a functionally improved shifting arrangement which can be manufactured at reasonable cost.
This object is achieved by having the shift finger equipped with an involute flank which is applied to a plane contact surface of the shift rail to be controlled. When the shift finger is applied to a plane contact surface of the shift rail to be controlled by an involute flank, a swivelling motion of the shift finger into a pushing motion of the shift rail with a transmission ratio which is constant over the swivelling angle can be obtained. If the shifting motion is introduced into the shifting arrangement by way of an exterior linearly controlled pivoted lever, a rising course is obtained on a graph, which plots the path ratio between the manual shift lever to be operated by the driver and the pushing path causing the gear synchronizing. Thus a desirable high leverage is available at the start of the synchronizing movement and a low leverage is available at the end.
It is desirable if involute flanks located on both sides of the shift finger, engage in a V-recess of the shift rail to be controlled and rest against the plane V-surfaces of the recess. The manufacturing of the shift rails having V-recesses of this type is simplified significantly and can be carried out at lower cost, particularly if hardened shift rails are used, which rails must be reground because of the unavoidable distortion due to hardening. A good response is obtained if the V-recess has an angle of approximately 60 degrees.
It is also advantageous if the locking system is provided by diametrically opposite stop cams that are mounted on the shift piece vertically and axially offset with respect to the shift finger. Circular outer contours of these stop cams will rest against the V-surfaces of the shift rails to be locked.
The transmission is provided with three shift rails, each being assigned to two transmission gears. These shift rails have shift lugs for engaging in shift forks which are longitudinally guided on a guiding tube. The guiding tube is in parallel with respect to the transmission shafts and the moveable shaft forks operate sliding sleeves which control the synchronizing clutches.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.